1. Field of the Invention
This invention relates to exhaust manifolds and, more particularly, to an insulated internal exhaust conduit for an exhaust manifold and a method of assembling same.
2. Description of the Prior Art
In modern engine technology and, in particular, for special use engines, such as unmanned marine engines, or stationary engines, and the like, turbochargers are used and are powered by the hot exhaust gases from the engine. It is desirable to convey the hot exhaust gases from the engine to the turbocharger in as high a temperature state as is possible. It is also desirable to maintain the outside temperature of the manifold below a predetermined temperature, such as below 400.degree. F. Heretofore, water jackets have been provided about exhaust pipes for the purpose of reducing the external surface temperature of the manifold and, at the same time, to prevent fires on unmanned engines. Unfortunately, the use of water jackets reduces the temperature of the exhaust gases, thereby reducing energy supplied to the hot exhaust gas turbocharger.
Some attempts have been made to produce a manifold with a surface temperature within allowable limits and, at the same time, to maintain the temperature of the exhaust gases as high as possible. One such system provides a sleeve inside the manifold which is surrounded by an air space which air space provides insulation for the hot exhaust gases to keep their temperature as high as possible and, at the same time, to reduce the amount of heat transmitted to the water of the water jacket. That system also provides for accommodating for the heat insulating sleeve increasing in diameter under the expansion caused by the hot exhaust gases. No provision is made for expansion of the heat insulating sleeve axially of the manifold. Axial expansion of the sleeve causes misalignment of the openings connecting the manifold to the exhaust ports of the engine and causes warping and distortion of the manifold. In addition, in at least one version of said prior device, the heat insulation sleeve is cast in place in the manifold which makes it almost impossible to replace the heat insulation sleeve when it deteriorates or fails.
In one other prior art device, insulation material is provided around a heat insulating sleeve and a specially designed sliding connection is provided between the sleeve and a tube extending from each exhaust port of the engine. These connections are complicated, expensive and almost impossible to maintain and service.
In another prior art device, heat insulation is provided between the inner sleeve and an intermediate sleeve, with the inner sleeve being capable of axial movement against specially designed collapsible gaskets located between adjoining ends of the sleeves.
Still another prior art device provides a manifold wherein the outer shell of the manifold is made in two parts which parts are assembled around an inner shell of the manifold so as to form a water jacket for cooling the inner shell with no insulation being provided for the inner shell.